Cargo Cult Science
From a Caltech commencement address given in 1974
Also in Surely You're Joking, Mr. Feynman!
During the Middle Ages there were all kinds of crazy ideas,
such as that a piece of of rhinoceros horn would increase potency.
Then a method was discovered for separating the ideas--which was to try
one to see if it worked, and if it didn't work, to eliminate it.
This method became organized, of course, into science. And it
developed very well, so that we are now in the scientific age.
It is such a scientific age, in fact, that we have difficulty in
understanding how witch doctors could ever have existed, when nothing
that they proposed ever really worked--or very little of it did.
But even today I meet lots of people who sooner or later get me
into a conversation about UFO's, or astrology, or some form of mysticism,
expanded consciousness, new types of awareness, ESP, and so forth. And
I've concluded that it's not a scientific world.
Most people believe so many wonderful things that I decided to
investigate why they did. And what has been referred to as my curiosity
for investigation has landed me in a difficulty where I found so much
junk that I'm overwhelmed. First I started out by investigating various
ideas of mysticism and mystic experiences. I went into isolation tanks
and got many hours of hallucinations, so I know something about that.
Then I went to Esalen, which is a hotbed of this kind of thought (it's a
wonderful place; you should go visit there). Then I became overwhelmed.
I didn't realize how MUCH there was.
At Esalen there are some large baths fed by hot springs situated
on a ledge about thirty feet above the ocean. One of my most pleasurable
experiences has been to sit in one of those baths and watch the waves
crashing onto the rocky slope below, to gaze into the clear blue sky above,
and to study a beautiful nude as she quietly appears and settles into the
bath with me.
One time I sat down in a bath where there was a beatiful girl
sitting with a guy who didn't seem to know her. Right away I began
thinking, "Gee! How am I gonna get started talking to this beautiful
I'm trying to figure out what to say, when the guy says to her,
"I'm, uh, studying massage. Could I practice on you?"
"Sure," she says. They get out of the bath and she lies down
on a massage table nearby.
I think to myself, "What a nifty line! I can never think of
anything like that!" He starts to rub her big toe. "I think I feel it,"
he says. "I feel a kind of dent--is that the pituitary?"
I blurt out, "You're a helluva long way from the pituitary, man!"
They looked at me, horrified--I had blown my cover--and said,
I quickly closed my eyes and appeared to be meditating.
That's just an example of the kind of things that overwhelm me.
I also looked into extrasensory perception, and PSI phenomena, and the
latest craze there was Uri Geller, a man who is supposed to be able to
bend keys by rubbing them with his finger. So I went to his hotel room,
on his invitation, to see a demonstration of both mindreading and bending
keys. He didn't do any mindreading that succeeded; nobody can read my
mind, I guess. And my boy held a key and Geller rubbed it, and nothing
happened. Then he told us it works better under water, and so you can
picture all of us standing in the bathroom with the water turned on and
the key under it, and him rubbing the key with his finger. Nothing happened.
So I was unable to investigate that phenomenon.
But then I began to think, what else is there that we believe?
(And I thought then about the witch doctors, and how easy it would have
been to check on them by noticing that nothing really worked.) So I
found things that even more people believe, such as that we have some
knowledge of how to educate. There are big schools of reading methods
and mathematics methods, and so forth, but if you notice, you'll see
the reading scores keep going down--or hardly going up--in spite of
the fact that we continually use these same people to improve the methods.
There's a witch doctor remedy that doesn't work. It ought to be looked
into; how do they know that their method should work? Another example
is how to treat criminals. We obviously have made no progress--lots
of theory, but no progress--in decreasing the amount of crime by the
method that we use to handle criminals.
Yet these things are said to be scientific. We study them.
And I think ordinary people with commonsense ideas are intimidated by
this pseudoscience. A teacher who has some good idea of how to teach
her children to read is forced by the school system to do it some other
way--or is even fooled by the school system into thinking that her method
is not necessarily a good one. Or a parent of bad boys, after disciplining
them in one way or another, feels guilty for the rest of her life because
she didn't do "the right thing," according to the experts.
So we really ought to look into theories that don't work, and
science that isn't science.
I think the educational and psychological studies I mentioned
are examples of what I would like to call cargo cult science. In the
South Seas there is a cargo cult of people. During the war they saw
airplanes with lots of good materials, and they want the same thing to
happen now. So they've arranged to make things like runways, to put
fires along the sides of the runways, to make a wooden hut for a man
to sit in, with two wooden pieces on his head to headphones and bars
of bamboo sticking out like antennas--he's the controller--and they wait
for the airplanes to land. They're doing everything right. The form
is perfect. It looks exactly the way it looked before. But it doesn't
work. No airplanes land. So I call these things cargo cult science,
because they follow all the apparent precepts and forms of scientific
investigation, but they're missing something essential, because the
planes don't land.
Now it behooves me, of course, to tell you what they're missing.
But it would be just about as difficult to explain to the South Sea
islanders how they have to arrange things so that they get some wealth
in their system. It is not something simple like telling them how to
improve the shapes of the earphones. But there is one feature I notice
that is generally missing in cargo cult science. That is the idea that
we all hope you have learned in studying science in school--we never
say explicitly what this is, but just hope that you catch on by all the
examples of scientific investigation. It is interesting, therefore,
to bring it out now and speak of it explicitly. It's a kind of scientific
integrity, a principle of scientific thought that corresponds to a kind
of utter honesty--a kind of leaning over backwards. For example, if
you're doing an experiment, you should report everything that you think
might make it invalid--not only what you think is right about it:
other causes that could possibly explain your results; and things you
thought of that you've eliminated by some other experiment, and how
they worked--to make sure the other fellow can tell they have been
Details that could throw doubt on your interpretation must be
given, if you know them. You must do the best you can--if you know
anything at all wrong, or possibly wrong--to explain it. If you make
a theory, for example, and advertise it, or put it out, then you must
also put down all the facts that disagree with it, as well as those that
agree with it. There is also a more subtle problem. When you have put a
lot of ideas together to make an elaborate theory, you want to make sure,
when explaining what it fits, that those things it fits are not just
the things that gave you the idea for the theory; but that the finished
theory makes something else come out right, in addition.
In summary, the idea is to give all of the information to help
others to judge the value of your contribution; not just the information
that leads to judgement in one particular direction or another.
The easiest way to explain this idea is to contrast it, for
example, with advertising. Last night I heard that Wesson oil doesn't
soak through food. Well, that's true. It's not dishonest; but the
thing I'm talking about is not just a matter of not being dishonest;
it's a matter of scientific integrity, which is another level. The
fact that should be added to that advertising statement is that no oils
soak through food, if operated at a certain temperature. If operated
at another temperature, they all will--including Wesson oil. So it's
the implication which has been conveyed, not the fact, which is true,
and the difference is what we have to deal with.
We've learned from experience that the truth will come out.
Other experimenters will repeat your experiment and find out whether
you were wrong or right. Nature's phenomena will agree or they'll
disagree with your theory. And, although you may gain some temporary
fame and excitement, you will not gain a good reputation as a scientist
if you haven't tried to be very careful in this kind of work. And it's
this type of integrity, this kind of care not to fool yourself, that is
missing to a large extent in much of the research in cargo cult science.
A great deal of their difficulty is, of course, the difficulty
of the subject and the inapplicability of the scientific method to the
subject. Nevertheless, it should be remarked that this is not the only
difficulty. That's why the planes don't land--but they don't land.
We have learned a lot from experience about how to handle some
of the ways we fool ourselves. One example: Millikan measured the charge
on an electron by an experiment with falling oil drops, and got an answer
which we now know not to be quite right. It's a little bit off because
he had the incorrect value for the viscosity of air. It's interesting to
look at the history of measurements of the charge of an electron, after
Millikan. If you plot them as a function of time, you find that one is a
little bit bigger than Millikan's, and the next one's a little bit bigger
than that, and the next one's a little bit bigger than that, until
finally they settle down to a number which is higher.
Why didn't they discover the new number was higher right away?
It's a thing that scientists are ashamed of--this history--because it's
apparent that people did things like this: When they got a number that
was too high above Millikan's, they thought something must be wrong--and
they would look for and find a reason why something might be wrong. When
they got a number close to Millikan's value they didn't look so hard.
And so they eliminated the numbers that were too far off, and did other
things like that. We've learned those tricks nowadays, and now we don't
have that kind of a disease.
But this long history of learning how to not fool ourselves--of
having utter scientific integrity--is, I'm sorry to say, something that
we haven't specifically included in any particular course that I know of.
We just hope you've caught on by osmosis
The first principle is that you must not fool yourself--and you
are the easiest person to fool. So you have to be very careful about that.
After you've not fooled yourself, it's easy not to fool other scientists.
You just have to be honest in a conventional way after that.
I would like to add something that's not essential to the science,
but something I kind of believe, which is that you should not fool the
layman when you're talking as a scientist. I am not trying to tell you
what to do about cheating on your wife, or fooling your girlfriend, or
something like that, when you're not trying to be a scientist, but just
trying to be an ordinary human being. We'll leave those problems up to
you and your rabbi. I'm talking about a specific, extra type of integrity
that is not lying, but bending over backwards to show how you're maybe
wrong, that you ought to have when acting as a scientist. And this is
our responsibility as scientists, certainly to other scientists, and I
think to laymen.
For example, I was a little surprised when I was talking to a
friend who was going to go on the radio. He does work on cosmology
and astronomy, and he wondered how he would explain what the applications
of his work were. "Well," I said, "there aren't any." He said, "Yes,
but then we won't get support for more research of this kind." I think
that's kind of dishonest. If you're representing yourself as a scientist,
then you should explain to the layman what you're doing-- and if they
don't support you under those circumstances, then that's their decision.
One example of the principle is this: If you've made up your
mind to test a theory, or you want to explain some idea, you should
always decide to publish it whichever way it comes out. If we only
publish results of a certain kind, we can make the argument look good.
We must publish BOTH kinds of results.
I say that's also important in giving certain types of government
advice. Supposing a senator asked you for advice about whether drilling
a hole should be done in his state; and you decide it would be better in
some other state. If you don't publish such a result, it seems to me
you're not giving scientific advice. You're being used. If your answer
happens to come out in the direction the government or the politicians
like, they can use it as an argument in their favor; if it comes out the
other way, they don't publish at all. That's not giving scientific advice.
Other kinds of errors are more characteristic of poor science.
When I was at Cornell, I often talked to the people in the psychology
department. One of the students told me she wanted to do an experiment
that went something like this--it had been found by others that under
certain circumstances, X, rats did something, A. She was curious as to
whether, if she changed the circumstances to Y, they would still do A.
So her proposal was to do the experiment under circumstances Y and see if
they still did A.
I explained to her that it was necessary first to repeat in her
laboratory the experiment of the other person--to do it under condition
X to see if she could also get result A, and then change to Y and see
if A changed. Then she would know the the real difference was the thing
she thought she had under control.
She was very delighted with this new idea, and went to her
professor. And his reply was, no, you cannot do that, because the
experiment has already been done and you would be wasting time. This
was in about 1947 or so, and it seems to have been the general policy
then to not try to repeat psychological experiments, but only to change
the conditions and see what happened.
Nowadays, there's a certain danger of the same thing happening,
even in the famous field of physics. I was shocked to hear of an
experiment being done at the big accelerator at the National Accelerator
Laboratory, where a person used deuterium. In order to compare his heavy
hydrogen results to what might happen with light hydrogen, he had to use
data from someone else's experiment on light hydrogen, which was done on
different apparatus. When asked why, he said it was because he couldn't
get time on the program (because there's so little time and it's such
expensive apparatus) to do the experiment with light hydrogen on this
apparatus because there wouldn't be any new result. And so the men in
charge of programs at NAL are so anxious for new results, in order to
get more money to keep the thing going for public relations purposes,
they are destroying--possibly--the value of the experiments themselves,
which is the whole purpose of the thing. It is often hard for the
experimenters there to complete their work as their scientific integrity
All experiments in psychology are not of this type, however.
For example, there have been many experiments running rats through all
kinds of mazes, and so on--with little clear result. But in 1937 a man
named Young did a very interesting one. He had a long corridor with doors
all along one side where the rats came in, and doors along the other side
where the food was. He wanted to see if he could train the rats to go in
at the third door down from wherever he started them off. No. The rats
went immediately to the door where the food had been the time before.
The question was, how did the rats know, because the corridor was so
beautifully built and so uniform, that this was the same door as before?
Obviously there was something about the door that was different from the
other doors. So he painted the doors very carefully, arranging the
textures on the faces of the doors exactly the same. Still the rats
could tell. Then he thought maybe the rats were smelling the food, so
he used chemicals to change the smell after each run. Still the
rats could tell. Then he realized the rats might be able to tell by
seeing the lights and the arrangement in the laboratory like any
commonsense person. So he covered the corridor, and still the rats
He finally found that they could tell by the way the floor
sounded when they ran over it. And he could only fix that by putting
his corridor in sand. So he covered one after another of all possible
clues and finally was able to fool the rats so that they had to learn
to go in the third door. If he relaxed any of his conditions, the rats
Now, from a scientific standpoint, that is an A-number-one
experiment. That is the experiment that makes rat-running experiments
sensible, because it uncovers that clues that the rat is really using--
not what you think it's using. And that is the experiment that tells
exactly what conditions you have to use in order to be careful
and control everything in an experiment with rat-running.
I looked up the subsequent history of this research. The next
experiment, and the one after that, never referred to Mr. Young. They
never used any of his criteria of putting the corridor on sand, or being
very careful. They just went right on running the rats in the same old
way, and paid no attention to the great discoveries of Mr. Young, and
his papers are not referred to, because he didn't discover anything about
the rats. In fact, he discovered all the things you have to do to
discover something about rats. But not paying attention to experiments
like that is a characteristic example of cargo cult science.
Another example is the ESP experiments of Mr. Rhine, and other
people. As various people have made criticisms--and they themselves
have made criticisms of their own experiements--they improve the techniques
so that the effects are smaller, and smaller, and smaller until they
gradually disappear. All the para-psychologists are looking for some
experiment that can be repeated--that you can do again and get the
same effect--statistically, even. They run a million rats--no, it's
people this time--they do a lot of things are get a certain statistical
effect. Next time they try it they don't get it any more. And now you
find a man saying that is is an irrelevant demand to expect a repeatable
experiment. This is science?
This man also speaks about a new institution, in a talk in which
he was resigning as Director of the Institute of Parapsychology. And, in
telling people what to do next, he says that one of things they have to do
is be sure the only train students who have shown their ability to get
PSI results to an acceptable extent--not to waste their time on those
ambitious and interested students who get only chance results. It is
very dangerous to have such a policy in teaching--to teach students only
how to get certain results, rather than how to do an experiment with
So I have just one wish for you--the good luck to be somewhere
where you are free to maintain the kind of integrity I have described,
and where you do not feel forced by a need to maintain your position
in the organization, or financial support, or so on, to lose your integrity.
May you have that freedom.
-- Richard Feynman